To maximize crop yield, it is important to be able to apply herbicides to weeds growing in tilled acreage in an effective way. There are various types of herbicides and devices for applying them, but cost and effectiveness determines the method used for killing particular types of weeds. One of the most effective types of herbicides which can be used is a non-selective herbicide, i.e. non-selective in that it kills whatever vegetation it comes in contact with. Of the various ways of applying non-selective herbicides to a field, one of the most effective is to directly apply the herbicide to the weed by rubbing a saturated applicator across its leaves, especially for grass type weeds. This eliminates losses due to evaporation from spraying, wasted herbicide distributed to other parts of the field, and crop destroyed by misapplied herbicide. Applying a non-selective herbicide to weeds with a saturated wiper is the most effective and least expensive way to kill weeds as maximum use is made of the most effective type of herbicide.
An example of a direct contact applicator using a wiper bar in the prior art is shown in U.S. Pat. No. 4,019,278 which includes two wiper bars adapted to be mounted to a hydraulic positioning assembly at the rear of a tractor. A first type of wiper bar includes a tube with a series of holes which permit the herbicide to leak through the tube and onto a covering of cloth or other wicklike material to provide a larger surface against which the weeds may rub. Alternately, the wiper bar may consist of a porous tubing which permits fluid to seep through the wall of the tube itself to maintain a film on the outer surface thereof. However, these wiper bars do not provide a controlled flow of herbicide and are not effective in transferring the herbicide to the weed.
In the first design, the herbicide has a tendency to saturate the portion of the wick immediately adjacent the hole and leak therethrough onto the ground. As the herbicide is permitted to flow by gravity through the holes and directly onto the wick covering the lower portion of the tube, an effective level of wick saturation can be achieved only for a small arcuate section of the bar. Not only does this limit the maximum flow rate of herbicide, and thereby the speed of a tractor through the field while applying it, it also greatly diminishes the effectiveness of the bar in applying the herbicide to the vegetation.
In the second design wiper bar, insufficient quantities of herbicide flow by osmosis through that portion of the pipe or tubing below the fluid level, and the smooth outer surface of the tube encourages the formation of rivulets of herbicide which trickle off the wiper bar. Thus, neither design provides a wiper bar with a substantial arcuate portion thereof being saturated with herbicide.
Furthermore, there is no means to control the flow of herbicide through either design, although the patentee suggests that the flow may be controlled by a metering valve. If the herbicide is present in the tube, then it will either seep through the holes in the tube or flow by osmosis through the walls of the tube at a rate determined by the physical parameters of the bar, such as the dimensions of the holes and the porosity of the tube wall and only slightly by the level of fluid in the tube. Changing the setting of a metering valve upstream from the tube is ineffective in controlling the flow of herbicide. As there is air in the system which eliminates any hydraulic action, the metering valve must be open wide enough to maintain a sufficient head in the tube to ensure a uniform distribution along the length of the tube. In other words, the metering valve must be open wide enough to meet the flow requirements of the tube design or the tube will run dry. If open too wide, the tube merely fills up and creates a back pressure which limits flow through the valve. Thus, herbicide flow is determined only by the size of the holes or the rate of osmosis inherent in the tube material.
Applicant has succeeded in developing a novel wiper bar and herbicide applicator system which solves the problems of the prior art. Applicant's wiper bar system includes a novel design for a wiper bar having a tube with a series of spaced apart holes along its bottom, a layer of wicklike material surrounding the lower two-thirds of the tube, an impermeable shield surrounding the lower one-half of the tube and wick, and a final layer of absorbent material surrounding the entire assembly. The wick, which may be felt or the like, is saturated by the herbicide as it flows out of the tube and spreads upwardly inside the shield through both hydraulic and capillary action. The impermeable shield which may be made of plastic or the like prevents herbicide from saturating the wick at just the lower end of the tube and dripping onto the field. As the wick covers more of the tube's circumference, it emerges from between the shield and tube on both sides thereof and directly contacts the absorbent outer layer above the mid-point and on both sides of the tube. Thus, the liquid first contacts the outer layer at both the front and rear, and along its upper portion. This is a particularly efficient scheme for saturating the majority of the outer layer and ensuring an even distribution of liquid throughout.
In applicant's first embodiment, a flexible plastic sheet is used as the shield and twine is closely coiled around the shield and tube to form the outer absorbent layer. The twine provides a durable, roughened surface for wiping the vegetation and also provides the necessary strength to hold the assembly together. In a second embodiment, a rigid plastic pipe half with chamfered or tapered edges is used as the shield and is clamped to the tube and wick with stainless steel pipe clamps. In this embodiment, burlap may be wrapped around and form the outer absorbent layer with a loose coil of twine used to hold the burlap in place. The rigid pipe half provides the necessary support for itself and the wick so that the burlap can be easily removed and the wiper bar disassembled for inspection and/or repair in the field.
Applicant's wiper bar design is adapted for hydraulically controlling the flow of herbicide therethrough which represents a significant improvement over the prior art. The wiper bar is filled completely with herbicide and air is bled from the system so that the flow and pressure of herbicide through the wiper bar is controlled by the height of the reservoir with respect to the wiper bar. The higher the reservoir, the greater the pressure and flow of herbicide through the wiper bar. Thus, the flow of herbicide through applicant's wiper bar can be effectively controlled, unlike the prior art.
One or more wiper bars may be mounted on the front end of a tractor and, unlike the prior art, the tractor may be driven forward through the field to apply the herbicide to the weeds. Applicant has found that his system is particularly helpful in eliminating Johnson grass from soybean fields by applying any suitable, non-selective herbicide such as Monsanto's ROUNDUP.sup.TM. Although applicant discloses this system for use with herbicides and weeds, it is apparent that applicant's system could also be used to apply insecticides, fungicides, or any other liquid directly to any stand of vegetation, either the growing crop, or the undesired weed.